1. Field of the Invention
The present invention relates to an information recording and/or reproducing apparatus to which a principle of a scanning tunnel microscope is applied.
2. Related Background Art
A scanning tunnel microscope (STM) is a recent development which is capable of directly observing an electron structure of surface atoms in a conductive material (G. Binnig et al. Phys. Rev. Lett, 49, 57 (1982)). The STM allows observation of a real space image with an extremely high resolving power, both for a single crystal and for an amorphous substance. The STM uses a tunnel current which flows if a probe and a conductive substance are brought close to each other, for example a distance of about 1 nm with a voltage being applied therebetween. The electric current changes exponentially in response to a change of distance between the probe and the conductive substrate. Thus if the probe is scanned to keep the tunnel current constant, a surface structure of real space may be observed with a resolving power on the order a atom. Although an analysis using the STM is limited to a conductive material, its applications also apply to structural analysis of a thin insulating layer formed on a surface of a conductive material. Further, since such apparatus and means use a method for detecting a micro electric current, the STM is advantageously used to observe a medium without any damage thereto, and with a low power consumption. Also, broad applications of STM use are expected because of its operability in air.
The utilization of STM a as a record reproduction apparatus of high density is known, for example as proposed in Japanese Laid-Open Patent Applications Nos. 63-161552 and 63-161553. The apparatus uses a probe similar to that used in the STM, and in which an applied voltage is changed between the probe and a recording medium to record data on the recording medium. The recording medium is a material having a switching property with memory in a voltage-current property, for example a thin film layer of a material selected from chalcogenides and .pi.-electron organic compounds. The reproduction is based on a difference of tunnel resistance between a region thus recorded and a region not recorded. Also, the recording and reproduction is possible with a recording medium in which recording is achieved by changing a surface shape of the recording medium by applying a voltage to the probe.
Another recording and reproducing apparatus is proposed in Japanese Laid-Open Patent Application No. 61-206148 using a STM, the semiconductor producing process technique for formation of the probe, and a processing techniques for making a fine structure on a single substrate (K. E. Peterson, "Silicon as a Mechanical Material", Proceedings of the IEEE, Vol. 70, p. 420, 1982). The apparatus is constituted such that a substrate is made of a single crystal silicon, parallel springs are formed by fine processing to be finely movable in a direction parallel to a surface of the substrate, i.e., in x, y-directions a tongue of a cantilevered beam with a probe formed thereon is provided on a moving part of the parallel spring, an electric field is applied between a torque and a base, and the probe may be displaced by an electrostatic force in a direction perpendicular to the substrate surface, i.e. in the z-direction.
Similarly, Japanese Laid-Open Patent Application No. 62-281138 describes a recording apparatus provided with a converter allay in which multiple tongues similar to that disclosed in the above Japanese Laid-Open Patent Application No. 61-206148 are arranged.
A memory capacity of the above apparatus can be considered to increase by increasing an area of the recording medium or by increasing the number of probe electrodes, to each of which an individual voltage may be applied. In order to move the probe electrodes over a broad region along the surface of the recording medium, an extremely high precision mechanism for coarse adjustment is required, in addition to a mechanism for fine adjustment, such as a cantilever. This presents a problem of scale increase of the overall apparatus. While, if the number of probe electrodes to which respective voltages are independently applied is simply increased to increase the memory capacity, wiring would be so complicated on the side of the probe electrodes and the number of wire connections would significantly increase in number. For example, in a case in which a mechanism for a fine adjustment is provided to independently displace the respective probe electrodes, an increase in wiring is necessary. Thus it is necessary to concentrate the entire wiring on the side of the probe electrodes. It is, therefore, an object of the present invention to provide an apparatus which can perform recording and reproduction of high density and large capacity, and which is simple in wiring and suitable for mass production, thus solving the above problems.
Further, there is a problem in the conventional apparatus that if a transfer rate of transferring information to be recorded is faster than a write speed, which is an addition of a write time of 1 bit, by a probe electrode and an access time for movement of probe electrode to a desired recording area, the transferred information cannot be recorded on the recording medium due to a mismatch caused between the information transfer rate and the write speed. This problem still exists in the case of plural probe electrodes provided in that the mismatch is caused between the information transfer rate and the write speed, though the write speed may be increased within a limited time. It is a further object of the present invention to provide an apparatus having plural probe electrodes, and which allows high speed writing with match a between the information transfer rate and the writing speed.